FIG. 1 depicts a schematic diagram of a portion of a typical wireless telecommunications system in the prior art, which system provides wireless telecommunications service to a number of wireless terminals (e.g., wireless terminals 101-1 through 101-3) that are situated within a geographic region. The heart of a typical wireless telecommunications system is Wireless Switching Center ("WSC") 120, which may also be known as a Mobile Switching Center ("MSC") or Mobile Telephone Switching Office ("MTSO"). Typically, Wireless Switching Center 120 is connected to a plurality of base stations (e.g., base stations 103-1 through 103-5) that are dispersed throughout the geographic area serviced by the system and to local and long-distance telephone and data networks (e.g., local-office 130, local-office 138 and toll-office 140). Wireless Switching Center 120 is responsible for, among other things, establishing and maintaining calls between wireless terminals and between a wireless terminal and a wireline terminal (e.g., wireline terminal 150), which is connected to the system via the local and/or long-distance networks.
The geographic area serviced by a wireless telecommunications system is partitioned into a number of spatially distinct areas called "cells." As depicted in FIG. 1, each cell is schematically represented by a hexagon; in practice, however, each cell usually has an irregular shape that depends on the topography of the terrain serviced by the system. Typically, each cell contains a base station, which comprises the radios and antennas that the base station uses to communicate with the wireless terminals in that cell and also comprises the transmission equipment that the base station uses to communicate with Wireless Switching Center 120.
For example, when wireless terminal 101-1 desires to communicate with wireless terminal 101-2, wireless terminal 101-1 transmits the desired information to base station 103-1, which relays the information to Wireless Switching Center 120 via wireline 102-1. Upon receipt of the information, and with the knowledge that it is intended for wireless terminal 101-2, Wireless Switching Center 120 then returns the information back to base station 103-1, again via wireline 102-1, which relays the information, via radio, to wireless terminal 101-2.
FIG. 2 depicts a block diagram of the architecture of a typical wireless telecommunications system in the prior art. Typically, each base station is connected to base station controller 201 via a separate and distinct wireline. Base station controller 201 can be, but is not necessarily, co-located with Wireless Switching Center 120.
For example, base station 103-1 is connected to base station controller 201 via wireline 102-1 and base station 103-3 is connected to base station controller 201 via wireline 102-3. Wirelines 102-1 and 102-3 can be fabricated from inexpensive and easily installed twisted-pair. In accordance with this architecture, each radio is located near the antennas with which it transmits and receives. In contrast, the emergence of another technology suggests removing the radios from the base stations and centralizing their functionality in a single unit known as a block radio.
A block radio is a digital signal processor that is programmed to multiplex, modulate, channel code, and upconvert one or more information-bearing signals using digital signal processing techniques. A block radio performs the same functionality as one or more traditional radios, but has several characteristics that are different than traditional radios. First, a traditional radio processes a single information-bearing signal. In contrast, a block radio is generally capable of processing a plurality of information-bearing signals simultaneously.
Second, a traditional radio is fabricated from radio-frequency components (e.g., capacitors, inductors, oscillators, etc.) and the processing of the information-bearing signal is performed by, and is largely defined by, the electrical characteristics of the components. In contrast, a block radio principally comprises a digital signal processor and the processing of the information-bearing signals is defined by software and software parameters.
Third, a change in the characteristics of a information-bearing signal (e.g., modulation scheme, bandwidth, etc.) can be implemented in a traditional radio by changing one or more of the radio-frequency components. In contrast, a change in the characteristics of a information-bearing signal can be implemented in a block radio by changing software and/or software parameters controlling the block radio. This enables a block radio to be re-defined and upgraded remotely via a telecommunications link.
Fourth, a block radio is generally less expensive than multiple traditional radios of comparable quality and processing power.
And fifth, because a block radio processes a plurality of information-bearing signals, it is capable of performing inter-information-bearing signal processing (e.g., diversity combining, beamforming, adjacent channel interference reduction, etc.) that a traditional radio, which sees only one information-bearing signal, is incapable of performing. Therefore, a block radio is more flexible, more powerful, less expensive and more-easily upgraded than the traditional radios that is capable of replacing.
FIG. 3 depicts a block diagram of a typical wireless telecommunications architecture in the prior art that incorporates block radio technology and that comprises: wireless switching center 120, baseband unit 301, radio heads 303-1 and 303-2, and wirelines 304-1 and 304-2. In accordance with this architecture, each geographically-dispersed base station of FIG. 2 is replaced with a radio head and baseband unit 301, which comprises block radio 302, is interposed between wireless switching center 120 and radio heads 303-1 and 303-2. Furthermore, in accordance with this architecture, block radio 302 interfaces with base station controller 201 and provides the functionality provided by the distributed traditional radios in the architecture of FIG. 2. Each of radio heads 303-1 and 303-2 comprises an amplifier and associated antenna.
In addition to the advantages provided by block radio 302, this architecture is advantageous because of the simple, uniform, and inexpensive design of the radio heads that it affords. The architecture in FIG. 3 is disadvantageous over the predecessor architecture in FIG. 2 in that the information-bearing signals transmitted between baseband unit 301 and radio heads 303-1 and 303-2 are at RF frequencies, which requires that wirelines 304-1 and 304-2 be fabricated from expensive and difficult-to-install coaxial cables. Furthermore, the fact that the signals transmitted between baseband unit 301 and radio heads 303-1 and 303-2 are at radio frequency considerably restricts the distance that baseband unit 301 can be from radio heads 303-1 and 303-2.
Therefore, the need exists for a wireless telecommunications system architecture that exhibits the advantages of block radio technology without the expense, distance limitation, and implementation difficulty associated with wirelines that are capable of transmitting signals at RF frequencies.